This invention relates to a transmission apparatus that sends and receives data divided into frames or packets, and more particularly to a bandwidth director used in a transmission apparatus that is connected physically or logically to plural terminal devices and houses multiplexed connections with the terminal devices to control the amount of data transmitted to the individual terminal devices. More specifically, this invention relates to a line termination device that is a subscriber line termination device for providing a connection line from a user's house, an office building, or a housing complex to a carrier's central office housing user lines, and that employs wavelength-division multiplexing or time-division multiplexing to multiplex data sent from a user terminal over an optical cable as an access line and to dynamically control which bandwidth is assigned according to a user's data transmission request.
The shift from xDSL to FTTH has increased the transmission capacity of an access line and led to diversification of information services provided over networks. Reasons behind this are an ever increasing density of data-based traffic such as Web browsing and downloading and a heightened demand for real-time traffic control in IP telephone services and the like.
The influence of service diversification is more prominent in an access line and an access network which are closer to user terminals than in a core network. In access-based infrastructure services, more complicated QoS control than ever is required depending on contracts made with users and the type of service. The QoS function determines for each packet a processing priority level in a packet network such that data that needs to be processed real-time more than other data is given a high priority level. However, priority levels that can be set in priority control are limited and it is difficult to process real-time packets always at a constant rate.
In other words, real-time data needs to be sent always at a constant rate (by sending a fixed amount of real-time data at a fixed timing) as in conventional telephone networks and in synchronous multiplexing communication networks using SDH (Synchronous Digital Hierarchy). This transmission control ensures stable communication quality and network management reliability in synchronous multiplexing communication networks. With QoS control, however, it is difficult to achieve this transmission control.
As has been described, service diversification has necessitated access network traffic control conditions which are classified roughly into two, one being strict communication timing control and the other being on-demand securing of a broad band. With the present access environment being a hybrid type that places an SDH network and an IP network both on the WAN side in a carrier's central office, this bipolar access-based traffic has to be multiplexed on an access line in order to improve the service quality of an access-based infrastructure. On the other hand, GE-PON (Gigabit Ethernet Passive Optical Network) is being put into practical use in concert with desynchronization of networks (proliferation of IP networks). IP networks and existing infrastructures, which are currently used in combination, are expected to be integrated into a next-generation network centered around a packet network. The compatibility with existing synchronous networks is an indispensable function to deal with this transition from synchronous networks and to provide wide area connection services during the network transition period.
Popularization of data communications has prompted standardization of GE-PON, which uses variable-length packets in an access network, and GE-PON is being introduced in more and more applications. Recently, there has been a large movement to replace conventional landline telephone services with those using IP networks (so-called IP telephones), and development of access networks based on Ethernet is progressing steadily. Ethernet is predicted to be a main technology for future access network development because of its ease of handling.
However, compared to conventional SDH networks, Ethernet is lacking in terms of network management functions. In addition, being a thoroughly best-effort packet communication network, Ethernet is easy to install at the expense of having difficulties in guaranteeing communication reliability. In near future where further service diversification makes networks indispensable information infrastructures, the demand for safety and security of communications as well as communication reliability is expected to increase. Until the reliability and safety of asynchronous communication networks are guaranteed, business activities in particular will continue to need synchronous communication networks which have conventionally been used in dedicated-line services and the like.
Following this trend, G-PON (Gigabit Passive Optical Network) systems, which are regulated by ITU-T G.984, too, are demanded to contain both fixed bandwidth communication data (synchronous multiplexing frames) over E1 or T1 lines which have conventionally been used in dedicated-line services and variable bandwidth data (asynchronous variable-length frames) of Ethernet which is used in data services. It is important in this type of multiplexing to ensure the quality of fixed bandwidth communications (used for voice communications or the like).